Shock strut



May l0, i949. F. E. BACHMAN SHOCK STRUT Filed May 26, 19414 Patented May10, 1949 SHQCK STRUT Fred E. Bachman, Chicago, lll., assignor toAmerican Steel Foundries, Chicago, lll., a corporation of New JerseyApplication May 26,1944, Serial N0. 537,478

22 Claims. (Cl. 267-64) My invention relates to shock absorbers and moreparticularly to an hydraulic device commonly termed an oleo strutandutilized in the connection between the fuselage and landing gear ofan aircraft. l

The primary object of my invention is to design a novel oleo strut ofthe type in which a hollow piston re'ciprocates within a cylindercarrying a metering pin which in turn reciprocates Within a passagethrough the piston head communicating with an internal chambertherewithin, the metering pin being of tapered cross-sectional area todene with said passage an orifice of gradually decreasingcross-sectional area through which hydraulic fluid within the device ismetered on the closure stroke thereof.

. My novel strut is so constructed that the piston head passage and theassociated metering pin are relatively movable, as the resultl ofinertia during vertical movement of the device as the craft to which itis attached passes over irregularities in the terrain or water. By meansof this arrangement, the cross-sectional area of the orice defined bythe pin and the piston head passage is momentarily increased in responseto vertical movement of the strut as a unit, thus lessening theresistance thereof to its closure stroke and thereby softening the shockto the associated craft.

Another object of my invention is to design a strut of the above type inwhich the metering pin is slidably carried at all times by theassociated piston head passage and is provided with tapered grooves orfiutes defining with said passage an orifice through which the hydraulicfluid is metered on the closure stroke of the device.

A different object of my invention is to provide a novel dashpotconstruction for dampening the extension stroke of the device at the endof said stroke.

In the drawings,

Figurevl is a sectional viewthrough a novel expanded oleo strutembodying my invention, portions of the device being shown in elevation.

Figure 2 is a sectional view comparable to Figure 1 but illustrating thestrut at the end of the closure stroke thereof.

Figure 3 is a sectional view through the metering pin taken onthe line3--3 of Figure 1.

Figure 4 is a fragmentary view comparable to Figure 2, but illustratinga modification of my invention. n

Describing my invention in detail and referring first to the embodimentythereof illustrated in Figures 1-3 inclusive, the device comprises a top2 follower in the form of a hollow piston 2 including a bracket 4 at itsupper extremity for convenient connection to the fuselage of anassociated aircraft (not shown). The piston 2 comprises an internal lowpressure chamber 6 to' which compressed air may be admitted through thefitting 8 to afford an air spring operable to resist the closure strokeof the device, as will be clearly understood by those skilled in theart. The piston 2 includes a piston head I0 with a central cylindricalpassage I2 therethrough for the reception of a complementary meteringpin I4 mounted within Ithe cylinder I6 as hereinafter more particularlydescribed, said cylinder con- .stituting the bottom follower of thedevice and 2i, 22 by means of springs 26, 26 carried'by stud bolts 28,28 mounted on the piston head III. It will be understood by thoseskilled in the art that on the compression or closure stroke of thedevice, thehydraullc pressure within the high pressure chamber 20 isoperable in conjunction with the springs 26, 26 to urge the flapperplate 24 to its closed position, whereby the hydraulic fluid within thedevice is metered through the orifice defined by the passage I2 and themetering pin Il, as hereinafter particularlyA described. On theextension stroke of the device, the hydraulic pressure within the lowpressure chamber 6'exceeds that within the high pressure chamber 20 andis thus operable to move the flapper plate 24 to its open position, asseen in Figure 1, against the resistance of the springs 26, 26.' Thispermits the fluid. to fiow from the chamber 6 into the chamber 20through the passages 22,22, thus insuring rapid release or extension ofthe device, as is desirable under service conditions.

It may be noted that the metering'pin I4 is provided with a plurality oflongitudinally extending utes or grooves 30, 30 defining with the-passage I2 orifices through which the hydraulic fluid is metered fromthe high pressure chamber 20 into the low pressure chamber 6 on theclosure strokel of'the device, said flutes tapering `toward the lowerpiston-like portion 32 of the metering pin Il which is slidably fittedwithin the chamber 34 formed within the cylinder I6 at its lowerextremity, said chamber being dened by the cylindrical wall 36 on whichis threaded a cap 38 engageable at 40 with the upper extremity of thepiston-like portion 32 to limit upward movement of the metering pin I4relative to the cylinder I6.

The wall 36 is provided with openings 42, 42 adjacent the lowerextremity.y thereof through which pressure fluid may pass to act uponthe lower end of the portion 32 which is provided with a cylindricalmember 44 extending down-1 Wardly through an opening 46 in the bottom ofthe cylinder I6, said opening being provided with an oleo ring 48 ofconventional design to prevent leakage of hydraulic fluid. The portion32 is normally urged into engagement at 40 with the cap 38 by means of aspring 50, and in this lwardly therewithin are balanced by the hydraulicpressure tending to urge the metering pin downwardly. Thus, when thestrut is moved upwardly as a unit as the landing gear to which it isattached passes over an irregularity in the terrain, the inertia of themetering pin I4 causes the latter to compress the spring 50 in order topermit the cylinder |6 and the piston 2 to move upwardly with respect tothe metering pin I4. This action results in relative upward movement ofthe passage I2 with respect to the metering pin |4, thereby increasingthe cross-sectional area of the orifice dei-ined by said passage I2 andthe flutes 30, 30| which are flared toward their upper extremities, asheretofore described. Thus, when the aircraft to which the strut isattached passes over an irregularity in the terrain resulting in unusualupward movement of the strut and the associated landing gear, theorifice deilned by the passage I2 and the flutes 30, 30 is momentarilyenlarged, thereby cushioning the resultant shock to the associatedcraft.

It may be noted that while the above described construction of themetering pin and orifice is extremely useful in the illustratedarrangement in providing slidable guidance for the metering pin I4throughout the extension and closure stroke of the device, nevertheless,if desired, this feature may be eliminated and the metering pin may beformed as a solid conical member tapering toward the upper extremitythereof and being of less cross-sectional area from end to end thereofthan thepassage I2, aswill be clearly understood by those skilled in theart, inasmuch as the use of such a pin is conventional practice. Thecylinder I6 is provided at its upper end with a collar 52 within whichis positioned an annular packing gland 54 of conventional design and abearing 56 of brass or any other suitable metal, the bearing and packinggland being held in assembled relationship within the collar 52 by meansof a packing gland nut 58. A sleeve 60 is secured within the cylinder I6by means of a ring 62 compressed between the upper end of the sleeve andthe packing gland 54, said sleeve having a shoulder 64 seated against acomplementary shoulder, within the cylinder I6. The sleeve 60 denes withthe piston 2 an` annular chamber 66 which communicates with the lowpressure chamber 6 by means of openings 68,

4 68 through said piston, and it will be understood that on theextension stroke of the piston, as shown in vFigure 1, when the sleeve60 moves within the portion of the passage 66 beneath the openings 68,68, hydraulic fluid is entrapped within said portion of the passage 66,which thus may be regarded as a dashpot chamber 10 (Figure 1). Theentrapped fluid is gradually metered through the openings 68, 68 throughthe space between the sleeve 60 and the adjacent wall of the piston 2,thus dampening the extension stroke of the device at the end of saidstroke wherein the sleeve 60 bears as at 12 (Figure 1) against a portionof the piston head I0.

Referring now to Figure 4 which is a Vfragmentary sectional viewcomparable to the lower portion of Figure 2, the cylinder |02 isprovided at its lower extremity with a closure |04 including an annularwall |06 deilning a` cylindrical chamber |08 within which is slidablyfitted the piston-like extremity IIO of the metering pin generallydesignated |I2. The upper extremity of the chamber |08 is closed by anut ||4 having a central opening II6 through which the metering pin I|2is slidably fitted, the engagement between the pin and the opening I I6being made substantially fluid tight by means of an oil ring II8. Thepiston-like portion IIO of the metering pin is urged by means of aspring |20 to its uppermost position in engagement as at |22 with thenut I I4, and it will be understood that the spring |20 is so designedas to be strong enough to resist the maximum iluid pressure within thelow pressure chamber |24, which pressure is operable to urge themetering pin downwardly relative to the cylinder |02 however, the spring|20 is nevertheless weak enough to permit the metering pin ||2 to movedownwardly against the resistance of the spring whenever the forceexerted thereagainst by means of the inertia of the metering pin duringrelative upward movement of the strut as a unit is sufficient toovercome the resistance ofthe spring |20.

The piston generally designated |26 is substantially identical with thatillustrated in Figures l and 2.

It may be noted that the piston-like portion ||0 of the metering pin isprovided with one or more passages |28 permitting the passage of airwithin the chamber |08 between the upper and lower extremities thereofas the metering pin reciprocates within said chamber under thecircumstances above described. A breather |30 may be provided within thelower extremity of the chamber |08 to permit free passage of air betweensaid chamber and the atmosphere externally thereof. Either the breather|30 or the passage |28 may be eliminated, if desired.

It is to be understood that I do not wish to be limited by the exactembodiments of the device shown which are merely by way of illustrationand not limitation as various and other forms of the device will, ofcourse, be apparent to those skilled in the art without departingfromthe spirit of the invention or the scope of the claims.

I claim:

1. In an hydraulic shock strut, a bottom follower in the form of acylinder comprising a high pressure chamber, a cylindrical metering pinchamber in the bottom of said cylinder, a cylindrical metering pin witha piston-like portion at one end thereof slidably fitted within saidchamber, abutment means for limiting movement of said portion outwardlywith respect to said second-mentioned chamber, resilient means foryieldingly urging said portion against said abutment means, a topfollower in the form of a hollow piston having an internal low pressurechamber and a head slidably tted within said high pressure chamber forvertical reciprocation therewithin, said head comprising a cylindricalopening affording communication between said high and low pressurechambers, said pin being slidably fitted at all times during extensionand closure of the strut within said opening, longitudinal flutes in theperimeter of said pin extending from a point adjacent said piston-likeportion thereof to the opposite extremity thereof and flaring towardsaid opposite extremity, a passage through said head spaced from saidopening and aording communication between said high and low pressurechambers, and a flapper plate resiliently mounted on said head withinsaid high pressure chamber for closing said passage on the closurestroke of the strut.

2. In an oleo strut, a bottom cylinder, a metering pin carried therebyand vertically movable with respect thereto, abutment means limitingrelative upward movement of said pin with respect to said cylinder,yielding means for urging a portion of said pin against said abutmentmeans, said yielding means being so formed and arranged as toaccommodate relativeupward movement of said cylinder with respect tosaid pin because of the inertia thereof during upward movement of saidstrut, a hollow piston reciprocal within said cylinder and comprising aninternal chamber and a piston head with an orifice within which said pinis slidably fitted, said orifice communicating with said chamber,passages in the sides of said pin extending longitudinally thereof tothe upper extremity thereof, said passages tapering in crosssectionalarea from said extremity, and flapper valve means for accommodatingpassage of hydraulic fluid from the interior of said piston to' saidcylinder on the extension stroke of the strut,

said valve means being operable on the closure stroke of the strut toprevent passage of hydraulic uid from said cylinder to the interior ofsaid piston.

3. In an oleo strut, a bottom cylinder, a metering pin carried therebyand vertically movable with respect thereto, abutment means limitingrelative upward movement of said pin with respect to said cylinder,yielding means for urging a portion of said pin against said abutmentmeans,

said yielding means being so formed and arranged `as to, accommodaterelative upward movement of said cylinder with respect to said pinbecause of the inertia of the pin during upward movement of said strut,and a hollow piston reciprocal within said cylinder and comprising aninternal charnber and a piston head with an orifice within which saidpin is slidably fitted, said orifice communicating with said chamber.

chamber for urging said portion into engagement with said abutmentmeans, a top follower in the form of a hollow piston having an internalchamber and a head slidably tted within said cylin- 'der forreciprocation therewithin, said head having a cylindrical openingcommunicating with said last-mentioned chamber, said pin Vbeingslidably' spect to said cylinder, yielding means for urging opening.

a portion of said pin against said abutment means, said yielding meansbeing so formed and arranged as to accommodate relativeupward movementof said cylinder with respect to said pin because of the inertia thereofduring sudden upward movement of said strut as a unit, a hollow pistonreciprocal within said cylinder and comprising an internal chamber and apiston head with an orifice within which said pin is slidably reciprocalat all times during extension and closure of the strut, said orificecommunicating with said chamber, passages in the sides of said pinextending longitudinally thereof from a point adjacent said po.tion tothe upper extremity of said pin, said passages tapering incross-sectional area from said upper extremity, and a compressed airspring in the upper extremity of said chamber for resiliently resistingthe closure stroke of said strut.

6. In an hydraulic shock strut, a bottom follower in the form of acylinder, a cylindrical metering pin 'chamber in the bottom of saidcylinder, a cylindrical metering pin with a piston-like portion at oneend thereof slidably fitted within said chamber, means for limitingrelative upward movement of said portion with respect to said chamberfor vertical reciprocation therewithin, a spring in said chamber bearingagainst abutment means on said portion and the bottom of siad chambenatop follower in the form of a hollow piston having a head reciprocalwithin said cylinder, said head comprising a cylindrical opening, saidpin being slidably tted at all times within said opening, longitudinalflutes in the perimeter of said pin extending from a point adjacent saidportion to the opposite end of said pin and viiaring toward saidopening, and resilient means compressible on the closure stroke of saidstrut and operable to return said t op follower to its normal extendedposition. Y

7. In an hydraulic shock strut, a bottom follower in the form vof acylinder, a cylindrical metering pin chamberin the bottom of vsaidcylinder, a metering pin with'a piston-like portion at one end thereofslidably jtted within said chamber,k abutment means for limitingrelativeupward movement of saidV portion with respect to said chamber, resilientmeans ,housed within said chamber for yieldinglyurging said portionagainst said' abutment means, a topy follower in the form of a hollowpiston having a head reciprocal within said cylinder and comprising an.opening affording communication of hydraulic fluid between saidcylinderand the interior of said ,piston saidpin being tapered incross-sectionalI area-from said piston-like portionv thereof' to ,theopposite" extremity thereof and being reciprocalfwithin said 8. Invianoleo strut, a vbottom cylinder metering pin carried therebyy andvertically, Imovable with respect thereto, abutment' means limitingrelative upward movement of said pin with respect to said cylinder,yielding means for urging a portion of said pin against said abutmentmeans, said yielding means being so formed and arranged as toaccommodate relative upward movement of said cylinder with respect tosaid pin because of the inertia thereof during upward movement of saidstrut, a hollow piston reciprocal within said cylinder and comprising aninternal chamber and a piston head with an orifice within whichsaid pinis slidably tted, said orifice communicating with said chamber, andpassages in the sides of said pin extending longitudinally thereof tothe upper extremity thereof, said passages tapering in cross-sectionalarea from said extremity.

9. In an oleo strut, a bottom cylinder, a metering pin carried therebyand vertically movable with respect thereto, abutment means limitingrelative upward movement of said pin with respect to said cylinder,yielding means for-urging a portion of said pin against said abutmentmeans, said yielding means being so formed and arranged as toaccommodate relative upward movement of said cylinder with respect tosaid pin because of the inertia thereof during upward movement of saidstrut, and a hollow piston reciprocal within said cylinder andcomprising an internal chamber and a piston head with an orifice withinwhich said pin is reciprocal, said orifice communicating with saidchamber, saidA pin tapering longitudinally thereof in cross-sectionalarea.

10. In an oleo strut, a cylinder, a cylindrical metering pin carriedthereby, a hollow piston reciprocal withinsaid cylinder and comprising ahead slidably fitted therein, a central cylindrical opening through saidhead communicating with being slidably fitted at all times duringclosure and extension of said strut within said opening, longitudinalgrooves in the cylindrical perimeter of said pin extending from one endthereof toward its connection with said cylinder, said grooves ilaringtoward said extremity, said pin being capable of vertical movement withrespect tosaid cylinder, stop means carried by the cylinder for limitingvertical movement of the pin with respect thereto, and yielding meansfor urging said pin into engagement with said stop means, said yieldingmeans being formed and arranged to accommodate said movement duetoinertia of said pin during sudden vertical movement of said strut.

11. In an hydraulic shock strut, top andV bottom followers, one of saidfollowers being a cylinder carrying a metering pin, and the other ofsaid followers being a hollow piston with an internal low pressurechamber and a piston head slidably fitted within said cylinder to definea high pressure chamber therein, said piston head comprising an openingaffording fluid connection between said chamberssaid pin tapering incrosssectional area from its connection with said cylinder and beingreciprocal Within said opening, a spring entirely independent ofpressure exerted in said high pressure chamber by associated hydraulicfluid therein, said spring accommodating, but yieldingly resisting,relative vertical movement between said pin and said cylinder as theresult of inertia of said pin duringv unusual vertical movement of saidstrut and irrespective of the relative positions of said piston andcylinder, and a compressed air spring in theupper extremity of saidlowpressure chamber for yieldingly resisting the closure stroke of saidstrut.

' a chamber within said piston, said metering pin 12. In an hydraudicshock strut, a bottom follower in the form of a cylinder carrying ametering pin, a top follower in the form of a hollow piston with aninternal low pressure chamber and a piston head reciprocal within saidcylindery to dene one end of va high pressure chamber therein, said headcomprising an opening affording means of fluid communication betweensaid chambers, said -pin being reciprocal within said opening anddefining therewith an orice, and spring means accommodatingbutyieldingly resisting, relative. vertical movement between said pin andsaid cylinder as the result of inertia of said pin during suddenvertical movement of saidstrut and irrespective of the relativepositions of said piston and said cylinder, said spring means being atall times substantially free from pressure exerted by associatedhydraulic uid in said high pressure chamber.

13. In an hydraulic shock strut, a bottom follower in the form of acylinder, a cylindrical metering pin chamber in the bottom of saidcylinder, a cylindrical metering pin with a pistonlike portion at oneend thereof slidably fitted within said chamber for verticalreciprocation therewithin, a spring in said chamber bearing againstabutment means on said portion and the bottom of said chamber, a topfollower in the form of a hollow piston having a head reciprocal withinsaid cylinder, said head comprising a cylindrical opening, said pinbeing slidably tted at all times within said opening, and longitudinalflutes in the perimeter of said pin extending from a point adjacent saidportion to the opposite end of said pin and flaring toward said opening.

14. In an oleo strut, a cylinder, a metering pin carried thereby andvertically movable with respect thereto, abutment means limitingrelative upward movement of said pin with respect to said cylinder,yielding means for urging a portion of said pin against said abutmentmeans, said yielding means being so formed and arranged as toaccommodate relative upward movement of said cylinder with respect tosaid pin because of the inertia of the pin during upward movement ofsaid strut, a hollow piston reciprocal within said cylinder andcomprising an internal chamber and a piston head with an orifice withinwhich said pin is slidably fitted, said orifice communicating with saidchamber, said piston dening with the wall of said cylinder an annularchamber above said head communicating with said first-mentioned chamberthrough an opening in said piston, and a sleeve carried by said cylinderwithin said annular chamber, said sleeve bearing against said wall andbeing slightly spaced from said piston to define therewith an annulardashpot chamber when said piston is in its fully extended position, saidpiston head having abutment means engageable with said sleeve beneathsaid opening to limit the extension stroke of said piston.

15. In an hydraulic shock strut, a pair of followers, one of saidfollowers being a cylinder carrying a metering pin and the other of saidfollowers being a hollow piston with van internal low pressure chamberand a piston head defining a high pressure chamber within said cylinderand comprising an opening connecting said chambers, said pin varyinglongitudinally thereof in crosssectionai area and being reciprocalwithin said opening and defining therewith an orifice, and meansindependent of pressure within said high pressure chamber foraccommodating, and yieldingly resisting relative movement between saidpin 9.' and said .cylinder as the result of inertia of said l pin duringsudden vertical movement of said strut.

16. In an hydraulic shock strut, a bottom follower in the form of acylinder, a cylindricalA metering Apin chamber inthe bottom of saidcylinder, a cylindrical metering pin with a pistonlike portion at oneend thereof slidably fitted within said chamber for verticalreciprocation therewithin, a spring in said chamber bearing againstabutment means on said portion and the bottom of said chamber, a topfollower in the form of a hollow piston having a head reciprocal withinsaid cylinder, said head comprising a cylindrical opening, said pintapering in cross-sectional area from its connection with said cylinderand being slidably iltted at all times within said opening.

17. In an hydraulic shock strut, a follower in the form of a cylindercomprising a high pressure chamber, a casing in said cylinder at thebottom thereof and forming a cylindrical metering pin chamber, acylindrical metering pin with an enlarged pistonlike portion at one endthereof slidably fitted within the chamber of said casing, abutmentmeans on said casing for limiting relative upward movement of saidportion with respect to said casing and having a fluid passagecommunicating with said high pressure chamber and through which said'pinextends, resilient means in said chamber for urging said portion intoengagement with said abutment means, fluid passages in said casingcommunicating with -the lower extremity of said cylindrical chamber, ahollow piston reciprocal within said cylinder and comprising an internallow pressure chamber and a piston head with an oriilce communicatingwith said high and low pressure chambers, said pin Ibeing slidablyfitted at all .times within said oriflce during extension and closure ofsaid strut.

18. In a hydraulic shock strut, a followerin the form of a cylindercomprising a high pressure chamber, a casing in said cylinder at the'bottom thereof and forming a cylindrical metering pin chamber, acylindrical metering pin with an enlarged pistonlike portion at one endthereof slidably fitted within the chamber of said casing, abutmentmeans on said casing for limiting relative upward movement' of saidportion' with respect to said casing and having a fluid passagecommunicating with said high pressure chamber and through which said pinextends, resilient meansin said chamber for urging said portion intoengagement with said abutment means, fluid passages in said casingcommunicating with the lower extremity of said cylindrical chamber, ahollow piston reciprocal within said cylinder and comprising an internallow pressure chamber and a piston head with an oriflce communicatingwith said high and low pressure chambers, said pin tapering incross-sectional area between said pistonlike portion thereof and theopposite extremity thereof and being reciprocal within said orifice atall times during extension and closure of the strut.

19. In an hydraulic shock strut, a follower in the form of a cylindercomprising a fluid chamber, a casing in said cylinder at the bottomthereof and forming a cylindrical chamber, a cylindrical metering pinwith an enlarged pistonlike portion slidably fitted within said casing,abutment means at the upper end of said casing for limiting upwardmovement of said portion with respect to said casing and having anopening through which said pin extends, means confined between said -plnand said abutment means for preventing flow Cil ,10 of fluid betweensaid chambersl resilientmeans in said casing for urging said portioninto engagement with said abutment means, a passage within said portionfor the passage of fluid within said cylindrical chamber between thelower and upper extremities thereof on reciprocation of said pin,another follower comprising a hollow piston reciprocal within saidcylinder and a piston head with an oriilce communicating with said uidchamber, said pin being slidably fitted at all times within said oriflceduring extension and closure of said strut and tapering incross-sectional area between said pistonlike portion thereof and theopposite extremity thereof.

20. In an hydraulic shock strut, a follower in the form of a cylindercomprising a fluid chamber, a casing in said cylinder at the bottomthereof and forming a cylindrical chamber having an opening at the lowerend thereof, a cylindrical metering pin with an enlarged pistonlikeportion slidably fitted within said casing, abutment means at the upperend of said casing for limiting upward movement of said portion withrespect to said casing and having an opening through which said pinextends, means between said pin and said abutment means for preventingflow of fluid from said fluid chamber into said cylindrical chamber,resilient means in said casing for urging said portion into engagementwith said abutment means, another follower comprising a hollow pistonreciprocal within said cylinder and a piston head with anA orificecommunicating with said fluid chamber, said pin being slidably fitted atall times within said orifice during extension and closure of saidstrut.,

21. In an hydraulic shock strut, a follower in the form of a cylindercomprising a fluid chamber, a casing in saidcylinder at the lbottom4'thereof and forming a cylindrical chamber, a cylindrical metering pinwith an enlarged pistonlike portion slidably fitted within said casing,abutment means at the upper end of said casing for limiting upwardmovement of said portion with respect to said casing and having anopening through which said pin extends, means between said Din and saidabutment means for preventing flow oi fluid Vfrom said fluidchamber intosaid cylindrical chamber, resilientmeans in said casing for urging saidportion into engagement with said abutment means,- another followercomprising a hollow pislton reciprocal within said cylinder and a pistonhead on said piston reciprocal within said cylinder and defining theupper extremity of a high pressure chamber therewithin, lsaid headhaving an opening receiving said pin and deilning therewith an orificeconnecting said chambers, a spring carried by said cylinder andl adaptedto yieldingly resist upward movement of the cylinder relative to saidpin, the hydraulic pressure on the portion of said pin in said highpressure chamber being substantially equalized whereby during sudden vupward movement of 'said absorber the cylinder moves upwardly withrespect to said pin due to s u the inertia of said pin thereby varyingthe crosssectional area of said orice.

' FRED E. BACHMAN.

REFERENCES CITED The following references are of record in the tile ofthis patent:

UNITED STATES PATENTS Number Name Date 1,037,052 Rennie Aug. `27, 19121,956,668 Charles May 1, 1934 2,039,135 Waugh et al. Apr. 28, 1,9362,095,112

Number Number France Aug. 28, 1933

